[SOLVED] Extract motion fields from the nvidia Visionworks Motion estimator example

Extract motion fields from the nvidia Visionworks Motion estimator example

I am trying to extract the motion field from the visionworks example. i saw the post in the nvidia forum here but i still do not understand how to get the motion field.

The documentation says that the motion fiels is a vx_image with type NVX_DF_IMAGE2F32, this means there are two channels.

Someone know the meaning of each channel? I even realize that the size of the image is the half of the input images used to detect the movement.

In the nvidia post the moderator said " that value(x, y) is the motion of the point (x, y)", but i do not understand what this means.

I understand the concept explained "More precisely, for point(x, y) with field value(mx, my) in frame N. The matched point in the frame N-1 is (x+mx, y+my)."

but i could not match the result i get in the vx_image with these parameters.

Solution

After some research i found the meaning. I write the solution in case is useful for someone else:

Here my understanding using cv::Mat that can be easily used to draw the result.

// get the motion in vx_image format
vx_image MotionImage = ime.getMotionField();

//convert to cv::Mat (or GpuMat as you like...)
nvx_cv::VXImageToCVMatMapper map(MotionImage);
//cv::cuda::GpuMat MotionImageGpuMat = map.getGpuMat();
cv::Mat MotionImageMatMap = map.getMat();

//resize the motion map as it is the half of the original image used to compute the motion
cv::Mat MotionImageMat;
cv::resize(MotionImageMatMap,MotionImageMat,cv::Size(),2.0,2.0,cv::INTER_NEAREST);

//split in two channels
cv::Mat MotionImageMat_split[2];           
cv::split(MotionImageMat, MotionImageMat_split);

//MotionImageMat_split[0](x,y) -> contains the increment for the pixel (x,y) in width (columns) direction between the current and previous frame.
//   Example: if MotionImageMat_split[0] at pixel (x,y) is 5 means that the difference between the current and previous frame in the width (columns) direction is 5

//MotionImageMat_split[1](x,y) -> contains the increment for the pixel (x,y) in height (rows) direction between the current and previous frame.
//   Example: if MotionImageMat_split[0] at pixel (x,y) is 5 means that the difference between the current and previous frame in the height (rows) direction is 5